1. Field of the Invention
This invention relates to an apparatus and a method for precisely applying radioactive material onto a substrate, e.g. a brachytherapy device or the like. More particularly, the present invention relates to materials and processes for fabricating brachytherapy devices with precisely controlled amounts of radioactive or precursor materials in precisely controlled positions within such devices. The present invention marries two heretofore-disparate technologies,. namely those of inkjet printing and of the fabrication of devices for brachytherapy.
2. Description of Related Art
Inkjet printing is used to print a precise amount of ink on a substrate in a precisely defined pattern. Inkjet printheads operate by one of two methods: the so-called, "continuous inkjet" process ("CIJ"), and the "drop-on-demand" process ("DOD"). In DOD inkjet printing, there are two commonly used technologies by which ink droplet ejection is achieved. These technologies are thermal (or bubble-jet) inkjet printing and piezo-electric (or impulse) inkjet printing. In thermal inkjet printing, the energy for ink drop ejection is generated by resistor elements which are electrically heated. Such elements heat rapidly in response to electrical signals controlled by a microprocessor and create a vapor bubble which expels ink through one or more jets associated with the resistor elements. In piezo-electric inkjet printing, ink drops are ejected in response to the vibrations of a piezo-electric crystal. The piezo-electric crystal responds to an electrical signal. controlled by a microprocessor.
The localized treatment of tumors and other medical conditions by the interstitial implantation of radioactive materials is a recognized treatment modality of long standing. Radioactive implants are used to provide radiation therapy in order to destroy tumors or reduce or prevent the growth of tumors. Radioactive implants are also used to prevent the growth of microscopic metastatic deposits in lymph nodes that drain the region where a tumor has been removed. Implants are also used to irradiate the postoperative tumor bed after the tumor is excised. Implantation of radioactive sources directly into solid tumors for the destruction of the tumors is used in a therapy referred to as brachytherapy.
For example, U.S. Pat. No. 3,351,049 to Lawrence discloses the use of low-energy X-ray-emitting interstitial implants as brachytherapy sources. Such implants, especially those containing palladium (Pd-103) or iodine (I-125) as the radioactive therapeutic isotope, have proven to be highly effective against solid malignancies. Excellent results have been obtained when such devices have been used against early-stage prostate cancer. These devices, or "seeds," must be very small because they are typically placed in the diseased organ through a hollow needle. Once implanted in the organ, they are held in place by the surrounding tissue or stitched in place with an associated suture. A typical size for a permanent implant is a rod or cylinder 0.8 mm in diameter by 4.5 mm long. A temporary implant is typically inserted into the tissue to be treated through a hollow needle or a plastic sleeve and has approximately the same outside diameter as a permanent implant of about 0.8 mm.
An essential step in the fabrication of these tiny brachytherapy devices is the inclusion in each device of a small amount of a radioactive isotope. U.S. Pat. No. 4,323,055 to Kubiatowicz, 4,702,228 to Russell, 5,405,309 to Carden and 5,713,828 to Coniglione disclose technologies addressing the fabrication of brachytherapy devices. Technology disclosed in the aforementioned patents has been used to develop the processes presently used in the production of commercially available Pd-103 and I-125 seeds. The revenue from the sale of such seeds in the United States in 1997 is estimated to have been about sixty million dollars.
Notwithstanding the commercial success of present methods of brachytherapy device fabrication, the present technology does not provide ways of making brachytherapy devices that contain precisely controlled amounts of radioactive material so as to provide devices for specific orders or to provide treatment tailored to therapy requirements. Nor does it provide ways of making brachytherapy devices that contain precisely positioned amounts of radioactive material so at to provide devices with radiation fields of a controlled shape to meet therapy requirements. Nor does it provide ways of making individually produced brachytherapy devices so as to control wastage of radioactive material and meet the needs of individual customers. Nor does it provide ways of automating production of brachytherapy devices to reduce radiation exposure during manufacture, to reduce the fabrication time and to improve the uniformity of the finished product.